<!DOCTYPE html>
<html lang="en">

<head>
  <meta charset="UTF-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>rem布局</title>
</head>
<style>
  html {
    font-size: 10px;
  }

  div {
    font-size: 1rem;
  }
</style>

<body>
  <div>123</div>
</body>

</html>